Real World : Space WeatherThis NASA video segment looks at space weather andexamines the major ramifications space weather can have on Earth.

Space weather is the concept of changing environmental conditions in near-Earth space or the space from the Sun's atmosphere to the Earth's atmosphere. It is distinct from the concept of weather within the Earth's planetary atmosphere (troposphere and stratosphere).

Space Weather is the description of changes in the ambient plasma, magnetic fields, radiation and other matter in space. Much of space weather is driven by energy carried through interplanetary space by the solar wind from regions near the surface of the Sun and the Sun's atmosphere (chromosphere and corona). The term space weather is sometimes used to refer to changes in interplanetary (and occasionally interstellar) space.

Space weather has two focal points: scientific research and applications. The term space weather was not used until the 1990s. Prior to that time, activities now known as space weather were considered to be part of physics or aeronomy or space exploration.

History of Space Weather

For centuries people have noticed the aurora, which is caused by space weather, but did not understand it. Navigators in the Mediaeval Ages in Europe, using a lodestone as a magnetic compass, noted that occasionally the stone's direction was deflected from magnetic north. This was described in 1600 in De Magnete but was not understood to be caused by space weather until the 19th century.

Space weather affected the first electrical telegraphs in the 1840s in various areas at various times. The great solar storm of 1859 disrupted telegraph operations around the world, causing articles to be published in many major newspapers at that time. Richard Carrington correctly connected the disruption with a solar flare observed the day before, and a great deflection of the Earth's magnetic field (or geomagnetic storm) simultaneous with the telegraph disruption. With this connection, space weather, as we now know it, became a subject of academic research within the study of solar physics.

Kristian Birkeland explained the physics of the aurora by creating artificial aurora in his laboratory, and he also predicted the solar wind. With the introduction of radio for commercial and military uses, it was noted that periods of extreme static or noise occurred. Severe radar jamming during a large solar event in 1942 led to the discovery of solar radio bursts (radio waves which cover a broad frequency range, created by a solar flare), another aspect of space weather.

In the 20th century, the interest in space weather has expanded as military and commercial systems have come to depend on systems affected by space weather. Communications satellites are a vital part of global commerce. Weather satellite systems provide information about terrestrial weather. The signals from satellites of the Global Positioning System are used in a wide variety of commercial products and processes. Space weather phenomena can interfere with or damage these satellites or interfere with the radio signals to and from these satellites. Space weather phenomena can cause damaging surges in long electrical transmissions lines and expose passengers and crew of aircraft travel to radiation, especially on polar routes.

The 1957/58 International Geophysical Year (IGY) created an enormous increase in research into space weather. Ground-based data obtained during the IGY demonstrated that the aurora occurred in an auroral oval, a permanent region of luminescence 15 to 25 degrees in latitude from the magnetic poles and 5 to 20 degrees wide. In 1958, the Explorer I satellite discovered the Van Allen belts or regions of radiation particles trapped by the Earth's magnetic field. In January 1959, the Soviet satellite Luna 1 first directly observed the solar wind and measured its strength. In 1969, INJUN-5 (a.k.a. Explorer 40) made the first direct observation of the electric field impressed on the Earth's high latitude ionosphere by the solar wind. In the early1970s, Triad data demonstrated that permanent electric currents flowed between the auroral oval and the magnetosphere. From these and other fundamental discoveries, research into space weather has grown exponentially.

Within our own solar system, space weather is greatly influenced by the speed and density of the solar wind and the interplanetary magnetic field (IMF) carried by the solar wind plasma. A variety of physical phenomena are associated with space weather, including geomagnetic storms and substorms, energization of the Van Allen radiation belts, ionospheric disturbances and scintillation of satellite-to-ground radio signals and long-range radar signals, aurora and geomagnetically induced currents at Earth's surface. Coronal mass ejections and their associated shock waves are also important drivers of space weather as they can compress the magnetosphere and trigger geomagnetic storms. Solar energetic particles, accelerated by coronal mass ejections or solar flares, are also an important driver of space weather as they can damage electronics onboard spacecraft (e.g. Galaxy 15 failure), and threaten the lives of astronauts.

The term 'space weather' came into usage in the 1990s when it became apparent that the impact of the space environment on human systems demanded a more co-ordinated research and application framework. The purpose of the National Space Weather Program in the USA is to focus research on the needs of the commercial and military communities which are affected by space weather, to connect the research community to the user community, to create co-ordination between operational data centres and to create better definitions of what the user community needs are. The concept was turned into an action plan in 2000, an implementation plan in 2002, an assessment in 2006 and a revised strategic plan in 2010. A revised action plan will be released in 2011 and a revised implementation plan will be released in 2012. One part of the National Space Weather Program is to make users aware that space weather affects their business.

Effect of Space Weather on Space Systems

Spacecraft AnomaliesSpacecraft malfunction for a variety of reasons. Some malfunctions are reported but many are not reported. A few failures can be directly attributed to space weather; many more failures are suspected to have a space weather component; and many failures are unrelated to space weather.

One indicator that space weather is a significant driver of spacecraft failure is that 46 of the 70 failures reported in 2003 occurred during the October 2003 geomagnetic storm. The two most common adverse space weather effects on spacecraft are radiation damage and spacecraft charging. Radiation (high energy particles) passes through the skin of the spacecraft and into the electronic components. In most cases the radiation causes an erroneous signal or changes one bit in memory of a spacecraft's electronics (single event upsets). In a few cases, the radiation destroys a section of the electronics (single event latchup). Spacecraft charging is the accumulation of an electrostatic charge on a non-conducting material on the spacecraft's surface by low energy particles. If enough charge is built-up, a discharge (spark) occurs. Damage to the spacecraft is done by causing an erroneous signal to be detected and acted on by the spacecraft computer as if the signal came from the ground controller, or the electronics are damaged by a surge of electrical current.

A recent study indicates that spacecraft charging is the predominant space weather effect on spacecraft in geosynchronous orbit.

Spacecraft Orbit Changes The orbits of spacecraft in Low Earth Orbit (LEO) decay to lower and lower altitudes due to the resistance from the friction between the spacecraft's surface (i.e. drag) and the outer layer of the Earth's atmosphere (a.k.a. the thermosphere and exosphere). Eventually, a spacecraft's orbit will decay so much that it will fall out of orbit and crash to the Earth's surface.

Many spacecraft launched in the past couple of decades have the ability to fire a small rocket: (1) to increase the altitude to compensate for the decay and extend the lifetime in space (2) to re-enter the atmosphere and crash into the ocean, or (3) to change the orbit to avoid collision with other spacecraft. In order to accomplish the goal of firing a small rocket, very precise information about the orbit is needed.

A geomagnetic storm can cause an orbit change over a couple of days that otherwise would occur over a year or more. The geomagnetic storm adds heat to the thermosphere, the atmosphere rises, the atmospheric density where LEO spacecraft orbit increases and drag increases. The collision of the Iridium 33 and Cosmos 2251 in February 2010 has demonstrated the importance of having precise knowledge of all objects in orbit. If a credible collision prediction had been available, Iridium 33 had the capability to manoeuver out of the path of Cosmos 2251.

Effect of Radiation on Humans in Space The exposure of a human body to ionizing radiation has the same harmful effects whether the source of the radiation is a medical X- ray machine, a nuclear power plant or radiation in space. The degree of the harmful effect depends on the length of exposure and the energy density of the radiation. The ever-present radiation belts extend down to the altitude of manned spacecraft such as the International Space Station (ISS) and the Space Shuttle but the amount of exposure is within the lifetime exposure limit under normal conditions. During a major space weather event which includes a burst of solar energetic particles, the flux can increase by one to several orders of magnitude. There are areas within ISS where the thickness of the spacecraft surface and equipment can provide extra shielding and may keep the total dose absorbed within lifetime safe limits. For the Shuttle, such an event requires an immediate termination of the mission.

Space weather is the concept of changing environmental conditions in near-Earth space or the space from the Sun's atmosphere to the Earth's atmosphere. It is distinct from the concept of weather within the Earth's planetary atmosphere (troposphere and stratosphere).

Space Weather is the description of changes in the ambient plasma, magnetic fields, radiation and other matter in space. Much of space weather is driven by energy carried through interplanetary space by the solar wind from regions near the surface of the Sun and the Sun's atmosphere (chromosphere and corona). The term space weather is sometimes used to refer to changes in interplanetary (and occasionally interstellar) space.

Space weather has two focal points: scientific research and applications. The term space weather was not used until the 1990s. Prior to that time, activities now known as space weather were considered to be part of physics or aeronomy or space exploration.

Effects of Space Weather on Ground Systems

Disruption of GPS and other spacecraft signals The ionosphere bends radio waves in the same manner that water in a swimming pool bends visible light. When the medium through which the light or radio waves travel is disturbed, the light image or radio information is distorted and can become unrecognizable. The degree of distortion (scintillation) of a radio wave by the ionosphere depends on the frequency of the radio signal. Radio signals in the VHF band (30 to 300 MHz)can be distorted beyond recognition by a disturbed ionosphere. Radio signals in the UHF band (300 MHz to 3 GHz) will propagate through a disturbed ionosphere but a receiver may not be able to keep locked to the carrier frequency. The Global Positioning System uses signals at 1575.42 MHz (L1) and 1227.6 MHz (L2), which can be distorted by a disturbed ionosphere, and a receiver computes an erroneous position or fails to compute any position.

Because the GPS signals are used by a wide range of applications, any space weather event which makes GPS signals unreliable can result in a significant impact on society. For example the Wide Area Augmentation System (WAAS) operated by the Federal Aviation Administration is used as a precision navigation tool for commercial aviation in North America. It is disabled by every major space weather event. In some cases WAAS is disabled for minutes and in a few cases it has been disabled for a few days. Major space weather events can push the disturbed polar ionosphere 10 degrees to 30 degrees of latitude toward the equator and can cause large ionospheric gradients (changes in density over distances of 100's of km) at mid and low latitude. Both of these factors can distort GPS signals.Disruption of Long-Distance Radio Signals Radio waves in the HF band (3 to 30 MHz) (also known as the shortwave band) are bent so much by the ionosphere that they are reflected back in the same manner as a mirror reflects light. Since the ground also reflects HF waves, a signal can be transmitted around the curvature of the Earth to a distant station. During the 20th century, HF communication was the only method for a ship or aircraft far from land or a base station to communicate. With the advent of systems such as Iridium, there are now other methods of communications but HF is still considered to be critical because not all vessels carry the newer equipment, and even if the newer equipment is onboard, HF is considered a critical backup system.

Space weather events can create irregularities in the ionosphere that scatter HF signals instead of reflecting them and make HF communications over long distance poor or impossible. At auroral and polar latitudes, small space weather events which occur frequently disrupt HF communications. At mid-latitudes, HF communications are disrupted by solar radio bursts, by X-rays from solar flares (which enhance and disturb the ionospheric D-layer) and by TEC enhancements and irregularities during major geomagnetic storms, which are infrequent. Transpolar routes flown by airplanes are particularly sensitive to space weather, in part because of Federal Aviation Regulations requiring reliable communication over the entire flight. It is estimated to cost about $100,000 each time such a flight is diverted from a polar route.

Effect of Radiation on Humans at and near ground level The Earth's magnetic field guides cosmic ray and solar energetic particles to polar latitudes, and radiation particles enter the mesosphere and stratosphere. Cosmic rays at the top of the atmosphere shatter atmospheric atoms and create lower energy, but still harmful, radiation particles which penetrate deep into the atmosphere. All aircraft flying above 10 km (33,000 feet) altitude are exposed to a noticeable amount of radiation. The exposure is greater in polar regions than at mid-latitude and equatorial regions. Many commercial aircraft from Europe and North America to East Asia fly over the polar region. When a space weather event causes radiation exposure to exceed the safe level set by aviation authorities,the aircraft's flight path is deviated to avoid the polar region.

Ground Induced Current: electrical transmission, pipelines, etc A well known ground-level consequence of space weather is geomagnetically induced current, or ground induced current or GIC. GIC flows through the ground to depths of 20 km or more during geomagnetic storms. A well-known example of the adverse effect of a GIC event is the collapse of the Hydro-Québec power network on March 13, 1989. This was started by a failure of an overloaded transformer, which led to a general blackout, which lasted more than 9 hours and affected 6 million people. The geomagnetic storm causing this event was itself the result of a Coronal Mass Ejection, ejected from the Sun on March 9, 1989.

A large geomagnetic storm can affect electric power grids at all latitudes. A storm as large as the 1859 event could disable the entire electric power grid in Eastern Canada and Eastern United States. GICs enter power grids, pipelines and other conducting networks through grounding wires. Pipelines and other activities at high latitudes are affected by GIC driven by modest levels of auroral activity which occur almost daily. GICs associated with space weather can affect other systems such as geophysical mapping and hydrocarbon production.

Geophysical Exploration Air and ship-borne magnetic surveys can be affected by rapid magnetic field variations during geomagnetic storms. Geomagnetic storms cause data interpretation problems because the space-weather-related magnetic field changes are similar in magnitude to those of the sub-surface crustal magnetic field in the survey area. Accurate geomagnetic storm warnings, including an assessment of the magnitude and duration of the storm, allows for an economic use of survey equipment.

Geophysics and Hydrocarbon Production For economic and other reasons, oil and gas production often involves the directional drilling of well paths many kilometers from a single wellhead in both the horizontal and vertical directions. Accuracy requirements are strict, due to target size – reservoirs may only be a few tens to hundreds of meters across – and for safety reasons, because of the proximity of other boreholes. Surveying by the most accurate gyroscopic method is expensive, since it can involve the cessation of drilling for a number of hours. An alternative is to use a magnetic survey, which enables measurement while drilling (MWD). Near real time magnetic data can be used to correct the drilling direction and nearby magnetic observatories prove vital. Magnetic data and space weather forecasts can also be helpful in clarifying unknown sources of drilling error on an on-going basis.

Effect of Space Weather on Terrestrial Weather The amount of energy entering the troposphere and stratosphere from all space weather phenomena is trivial compared to the solar insolation in the visible and infra-red portions of the solar electromagnetic spectrum. However there does seem to be some linkage between the 11 year sunspot cycle and the Earth's climate. For example, the Maunder minimum, a 70 year period almost devoid of sunspots, correlates to a cooling of the Earth's climate. One suggestion for the linkage between space and terrestrial weather is that changes in cosmic ray flux cause changes in the amount of cloud formation. Another suggestion is that variations in the EUV flux subtly influence existing drivers of the climate and tip the balance between states such as the El Niño/La Niña. However, a linkage between space weather and the climate has not been demonstrated conclusively.

Observations of Space Weather

The observation of space weather is done both for scientific research and for applications. The type of observation done for science has varied over the years as the frontiers of our understanding have increased and due to competition for resources from other types of space-related research. The observations related to applications have been more systematic and have expanded over the years as awareness and applications have increased.

Observing Space Weather From the Ground

Presently, space weather is monitored at ground level by observing changes in the Earth's magnetic field over periods of seconds to days, by observing the surface of the Sun and by observing radio noise created in the Sun's atmosphere.

The Sunspot Number (SSN) is the number of sunspots on the Sun's photosphere in visible light on the side of the Sun visible to an Earth observer. The number and total area of sunspots are related to the brightness of the Sun in the extreme ultraviolet (EUV) and X-ray portions of the solar spectrum and to solar activity such as solar flares and coronal mass ejections (CMEs).

10.7 cm Radio Flux (F10.7) is a measurement of RF emissions from the Sun and is approximately correlated with the solar EUV flux. Since this RF emission is easily obtained from the ground and EUV flux is not, this value has been measured and disseminated continuously since 1947. The world standard measurements are made by the Dominion Radio Astrophysical Observatory at Penticton, B.C., Canada, and reported once a day at local noon in solar flux units (10-22W·m-2·Hz-1). F10.7 is archived by the National Geophysical Data Center.

Dst index is an estimate of the magnetic field change at the Earth's magnetic equator due to a ring of electrical current at and just earthward of GEO. The index is based on data from four ground-based magnetic observatories between 21 degrees and 33 degrees magnetic latitude during a one hour period. Stations closer to the magnetic equator are not used due to ionospheric effects. The Dst index is compiled and archived by the World Data Center for Geomagnetism, Kyoto.

Kp/ap Index: 'a' is an index created from the geomagnetic disturbance at one mid- latitude (40 degrees to 50 degrees latitude) geomagnetic observatory during a 3 hour period. 'K' is the quasi-logarithmic counter-part of the 'a' index. Kp and ap are the average of K and a over 13 geomagnetic observatories to represent planetary-wide geomagnetic disturbances. The Kp/ap index indicates both geomagnetic storms and substorms (auroral disturbance). Kp/ap is available from 1932 onward.

AE index is compiled from geomagnetic disturbances at 12 geomagnetic observatories in and near the auroral zones and is recorded at 1 minute intervals. The AE index is made public with a delay of two to three days, which severely limits its utility for space weather applications. The AE index indicates the intensity of geomagnetic substorms except during a major geomagnetic storm when the auroral zones expand towards the equators from the observatories.

Radio noise bursts are observed and reported by the Radio Solar Telescope Network to the U.S. Air Force and to NOAA. The radio bursts are associated with plasma from a solar flare interacting with the ambient solar atmosphere.The Sun's photosphere is observed continuously by a series of observatories for activity which can be the precursors to solar flares and CMEs.

The Global Oscillation Network Group (GONG) Project monitors both the surface and the interior of the Sun by using helioseismology, the study of sound waves propagating through the Sun and observed as ripples on the solar surface. GONG can detect sunspot groups on the far side of the Sun. This ability has recently been verified by visual observations from the NASA STEREO spacecraft.

Neutron Monitorson the ground indirectly monitor cosmic rays from the Sun and galactic sources. Cosmic rays do not reach the Earth's surface due to the shielding of the Earth's magnetic field and atmosphere. When cosmic rays interact with the atmosphere, atomic interactions occur which cause a shower of lower energy particles to descend deeper into the atmosphere and to ground level. The presence of cosmic rays in the near-Earth space environment can be detected by monitoring high energy neutrons at ground level. Small fluxes of cosmic rays are present continuously. Large fluxes are produced by the Sun during events related to energetic solar flares.Total Electron Content (TEC) is a measure of the ionosphere over a given location. TEC is the number of electrons in a column one meter square from the base of the ionosphere (approximately 90 km altitude) to the top of the ionosphere (approximately 1000 km altitude). Many of the measurements of TEC are made by monitoring the two frequencies transmitted by GPS spacecraft. Presently GPS TEC is monitored and distributed in real time from more than 360 stations maintained by numerous agencies in many countries.

Observing Space Weather With Satellites

After Explorer I discovered that space was not a void, many research spacecraft have been launched to discover and characterize the space environment. There have been too many spacecraft since then to list them all here and they have carried a wide variety of instruments.

The spacecraft of the Orbiting Geophysical Observatory series were among the first spacecraft with the mission of discovering the space environment. Significant recent spacecraft are the NASA-ESA Solar-Terrestrial Relations Observatory (STEREO) pair of spacecraft launched in 2006 into solar orbit, and Radiation Belt Storm Probes (RBSP) to be launched in 2012 into a highly elliptical Earth-orbit. The two STEREO spacecraft drift away from the earth by about 22 degrees per year, one leading and the other trailing the earth in its orbit. Together they compile information about the Sun's surface and atmosphere in three dimensions. RBSP will obtain detailed information about the radiation belts, geomagnetic storms and the relationship between the two.

The mission of most spacecraft is unrelated to gathering information about the space environment for research or applications, but some of these other spacecraft have carried auxiliary instruments or had some part of their primary payload used for space weather. Some of the earliest such spacecraft were part of the Applications Technology Satellite (ATS) series at GEO which were precursors to the modern Geostationary Operational Environmental Satellite (GOES) weather satellite and many communication satellites. The ATS spacecraft carried environmental particle sensors as auxiliary payloads and had their navigational magnetic field sensor used for sensing the environment.

Many of the earliest instruments used for monitoring the space environment were and are research spacecraft which were re-purposed or jointly purposed for space weather applications and forecasting. One of the first of these is the IMP-8 (Interplanetary Monitoring Platform). The IMP-8 orbited the Earth at 35 Earth Radii and observed the solar wind for two-thirds of its 12-day orbit from 1973 to 2006. Since the solar wind carries disturbances which affect the magnetosphere and ionosphere, IMP-8 demonstrated the utility of continuously monitoring the solar wind. IMP- 8 was followed by ISEE-3 which was placed near the L1 Sun-Earth Lagrangian point, 235 Earth radii above the surface (about 1.5 million km, or 924,000 miles) and continuously monitored the solar wind from 1978 to 1982. The next spacecraft to monitor the solar wind at the L1 point was WIND from 1994 to 1998. After April 1998, the WIND spacecraft orbit was changed to circle the Earth and pass by the L1 point occasionally.

The NASA Advanced Composition Explorer (ACE) has monitored the solar wind at the L1 point from 1997 to the present. It is estimated to cease operating in about 2024. Funding for a replacement for ACE is in the 2012 budget request for NOAA, with an planned launch in 2015. The replacement's primary mission will be space weather forecasting and applications.

In addition to monitoring the solar wind, monitoring the Sun is important to space weather. Because the solar EUV cannot be monitored from the ground, the joint NASA-ESA Solar and Heliospheric Observatory (SOHO) spacecraft was launched and has provided EUV images of the Sun from 1995 to the present. SOHO is a main source of near-real time solar data for both research and space weather prediction and inspired the STEREO mission. The Yohkoh spacecraft at LEO observed the Sun from 1991 to 2001 in the X-ray portion of the solar spectrum and was useful for both research and space weather prediction. Data from Yohkoh inspired the Solar X-ray Imager on GOES.

Spacecraft with instruments whose primary purpose is to provide data for space weather predictions and applications include the GOES series of spacecraft, the POES series, the DMSP series, and the Meteosat series. The GOES spacecraft have carried an X-Ray Sensor (XRS) which measures the flux from the whole solar disc in two bands - 0.05 to 0.4 nm and 0.1 to 0.8 nm since 1974, a X-ray imager (SXI) since 2004, a magnetometer which measures the distortions of the Earth’s magnetic field due to space weather, a whole disk EUV sensor since 2004, and particle sensors (EPS/HEPAD) which measure ions and electrons in the energy range of (50 keV to 500 MeV). Starting sometime after 2015, the GOES-R generation of GOES spacecraft will replace the SXI with a solar EUV image (SUVI) similar to the one on SOHO and STEREO and the particle sensor will be augmented with a component to extend the energy range down to 30 eV.

Space Weather Modelling

Space weather models are computer simulations of the space weather environment. Like computer models for meteorology, space weather models take a limited set of data values and extrapolate to values which describe the entire space weather environment or a segment of the space weather environment in the model. Each model makes a prediction or a set of predictions about how the environment evolves with time. Computer models use the sets of mathematical equations to describe the physical processes involved.

The early space weather models were heuristic; i.e. they relate one phenomenon with another without including any physics in the relationship. Some of these simple models are still used because they take minimal resources and yield results which are good enough for some purposes.

Present research and development efforts concentrate on complex sets of equations which account for as many elements of physics as possible.

Space weather models differ from meteorological model in that amount of input is vastly smaller and no single space weather model yet can reliably predict the environment from the surface of the Sun to the bottom of the Earth's ionosphere. A significant portion of space weather model research and development in the past two decades has been done as part of the Geospace Environmental Model (GEM) program of the National Science Foundation.

Two major centers for modeling are the Center for Space Environment Modeling (CSEM) and the Center for Integrated Space weather Modeling (CISM). The Community Coordinated Modeling Center (CCMC) at the NASA Goddard Space Flight Center is a facility for coordinating the development and testing of research models, for the improvement of models and for preparing models for transition to space weather prediction and application.

Modelling efforts to simulate the environment from the Sun to the Earth use several method including:

(a) magnetohydrodynamics in which the environment is treated as a fluid(b) particle in cell in which non-fluid interactions are handled within a cell and then a series of cells are connected together to describe the environment(c) first principles in which physical processes are in balance (or equilibrium) with one another, (d) semi-static modeling in which a statistical or empirical relationship is described

or a combination of several of these methods.

Examples of space weather events:

May 15-16, 1921: one of the largest geomagnetic storms caused the entire signal and switching system of the New York Central Railroad below 125th street in New York City to be put out of operation. Worldwide disruption of telegraph service.

August 7, 1972: a large Solar Energetic Particles event occurred. If astronauts had been in space at the time, the dose would have been deadly or at least life-threatening. Fortunately, this large event happened between the Apollo 16 and Apollo 17 lunar missions.

January 20, 1994: a geomagnetic storm temporarily disabled two Canadian communication satellites, Aniks E1 and E2 and the international communication satellite Intelsat K.

January 7, 1997: a Coronal Mass Ejection hit the Earth's magnetosphere on January 10 and caused the loss of the AT&T Telstar 401 communication satellite (a $200 million value).

April 21, 2002: the Nozomi Mars Probe was hit by a large Solar Energetic Particles event which caused large-scale failure. The mission, which was already about 3 years behind schedule, was eventually abandoned in December 2003.